Semiconductor Device and Method

ABSTRACT

In an embodiment, a device includes: a first reflective structure including first doped layers of a semiconductive material, alternating ones of the first doped layers being doped with a p-type dopant; a second reflective structure including second doped layers of the semiconductive material, alternating ones of the second doped layers being doped with a n-type dopant; an emitting semiconductor region disposed between the first reflective structure and the second reflective structure; a contact pad on the second reflective structure, a work function of the contact pad being less than a work function of the second reflective structure; a bonding layer on the contact pad, a work function of the bonding layer being greater than the work function of the second reflective structure; and a conductive connector on the bonding layer.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of U.S. Provisional PatentApplication No. 62/694,759, filed on Jul. 6, 2018, which application ishereby incorporated herein by reference.

BACKGROUND

The semiconductor industry has experienced rapid growth due to ongoingimprovements in the integration density of a variety of electroniccomponents (e.g., transistors, diodes, resistors, capacitors, etc.). Forthe most part, improvement in integration density has resulted fromiterative reduction of minimum feature size, which allows morecomponents to be integrated into a given area. Optical features havebeen integrated with semiconductor devices in increasingly moreapplications in recent years, particularly due to the rising demand forcameras in phones, tables, and other portable devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1 through 7 illustrate various cross-sectional view of a processfor forming laser devices, in accordance with some embodiments.

FIGS. 8 through 21 illustrate various cross-sectional view of a processfor forming a laser device package, in accordance with some embodiments.

FIG. 22 illustrates operation of a laser device package, in accordancewith some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In accordance with some embodiments, laser devices having contact padsare formed. The laser diodes of the laser devices are PIN diodes formedfrom a doped semiconductive material, such as doped GaAs. The contactpads and semiconductive material share an ohmic junction. Underbumpmetallurgies (UBMs) are formed on the contact pads before conductiveconnectors are electrically coupled to the laser devices. The UBMs helpprevent metal inter-diffusion between the contact pads and conductiveconnectors. As such, when reflowing the conductive connectors, thejunction of the contact pads and semiconductive material may retain itsohmic properties. Electrical connections of a low contact-resistance maythus be formed for the laser devices.

FIGS. 1 through 7 illustrate various cross-sectional view of a processfor forming laser devices, in accordance with some embodiments. A firststructure 100 is formed including a carrier substrate 102 having aplurality of laser devices 104 (see FIG. 7) formed thereon. The laserdevices 104 include single-frequency laser diodes. In the embodimentshown, the laser devices 104 include vertical-cavity surface-emittinglaser devices. It should be appreciated that the laser devices 104 mayinclude other types of diodes such as distributed Bragg reflector (DBR)laser diodes, light emitting diodes (LEDs), or the like.

In FIG. 1, a carrier substrate 102 is provided. The carrier substrate102 may be a semiconductor substrate, such as a bulk semiconductor, asemiconductor-on-insulator (SOI) substrate, or the like, which may bedoped (e.g., with a p-type or n-type dopant) or undoped. The carriersubstrate 102 may be a wafer, such as a silicon wafer. Generally, an SOIsubstrate is a layer of a semiconductor material formed on an insulatorlayer. The insulator layer may be, for example, a buried oxide (BOX)layer, a silicon oxide layer, or the like. The insulator layer isprovided on a substrate, typically a silicon or glass substrate. Othersubstrates, such as a multi-layered or gradient substrate may also beused. In some embodiments, the semiconductor material of the carriersubstrate 102 may include silicon; germanium; a compound semiconductorincluding silicon carbide, gallium arsenic, gallium phosphide, indiumphosphide, indium arsenide, and/or indium antimonide; an alloysemiconductor including SiGe, GaAs, GaAsAl, GaAsP, GaN, InGaP, AlAs,InP, GaP, InGaN, and/or InAlN; or combinations thereof. In a particularembodiment, the carrier substrate 102 is a GaAs substrate.

Further, one or more etch stop layer(s) 106 are formed on the carriersubstrate 102. In some embodiments, the etch stop layer(s) 106 areformed from a dielectric material, such as silicon carbide, siliconnitride, silicon oxynitride, or the like. In some embodiments, the etchstop layer(s) 106 are formed from a semiconductive material, such asInGaP, InP, GaAsAl, AlAs, or the like. The etch stop layer(s) 106 areselective to an etch process used to pattern subsequently formedreflective structures (see below), such that the carrier substrate 102may be protected during the etching processes.

Further, a first reflective structure 108 is formed on the etch stoplayer(s) 106. The first reflective structure 108 includes multiplelayers of materials, such as dielectric or semiconductive materials. Thelayers may be doped or undoped. The layers may be deposited by asuitable deposition process, such as chemical vapor deposition (CVD), ormay be grown by a suitable epitaxy process. The first reflectivestructure 108 may be a distributed Bragg reflector, which usesalternating layers of materials having different refractive indices toreflect light. In some embodiments, the first reflective structure 108includes alternating doped and undoped layers of the material of thecarrier substrate 102 (e.g., GaAs), with the doped layers havingdifferent refractive indices than the undoped layers. The dopant may beany dopant that allows the doped layers to have different refractiveindices than the undoped layers. In some embodiments, the dopant is ap-type dopant such as carbon. In some embodiments, the doped layers ofthe first reflective structure 108 have a dopant concentration in therange of from about 1E15 atoms/cm³ to about 1E21 atoms/cm³. The firstreflective structure 108 may thus form p-type reflecting regions in theresulting laser diodes.

Further, an emitting semiconductor region 110 is formed on the firstreflective structure 108. The emitting semiconductor region 110 alsoincludes a doped layer of the material of the carrier substrate 102(e.g., GaAs). The emitting semiconductor junction 110 has a p-typeregion and a n-type region, and forms a P-N junction that lases at asingle resonant frequency during operation. The p-type region may bedoped with p-type dopants such as boron, aluminum, gallium, indium, andthe like. The n-type region may be doped with n-type dopants such asphosphorus, arsenic, and the like. In some embodiments, the p-typeregion is formed over the n-type region. The n-type region of theemitting semiconductor region 110 may be connected to the firstreflective structure 108 such that light emits towards the firstreflective structure 108.

Further, a second reflective structure 112 is formed on the emittingsemiconductor region 110. The p-type region of the emittingsemiconductor region 110 may be connected to the second reflectivestructure 112. The second reflective structure 112 includes multiplelayers of materials, such as dielectric or semiconductive materials. Thelayers may be doped or undoped. The layers may be deposited by asuitable deposition process, such as CVD, or may be grown by a suitableepitaxy process. The second reflective structure 112 may be adistributed Bragg reflector, which uses alternating layers of materialshaving different refractive indices to reflect light. In someembodiments, the second reflective structure 112 includes alternatingdoped and undoped layers of the material of the carrier substrate 102(e.g., GaAs), with the doped layers having different refractive indicesthan the undoped layers. The dopant may be any dopant that allows thedoped layers to have different refractive indices than the undopedlayers. In some embodiments, the dopant is a n-type dopant such assilicon. In some embodiments, the doped layers of the second reflectivestructure 112 have a dopant concentration in the range of from about1E15 atoms/cm³ to about 1E21 atoms/cm³. The second reflective structure112 may thus form n-type reflecting regions in the resulting laserdiodes. The dopant of the second reflective structure 112 may be adifferent dopant than the dopant of the first reflective structure 108.

The reflective structures 108 and 112 form a resonant cavity, to helpenhance the intensity of light from the emitting semiconductor region110. The reflective structures 108 and 112 have different reflectivity,e.g., the refractive indices of the reflective structures 108 and 112are different. In some embodiments, the first reflective structure 108is formed to have a lower reflectivity than the second reflectivestructure 112, to allow emission of a laser beam from the emittingsemiconductor region 110. The refractive indices of the reflectivestructures 108 and 112 may be varied by adjusting the overall height andoverall doping amount of the reflective structures 108 and 112. Forexample, the height H₁ of the first reflective structure 108 may be lessthan the height H₂ of the second reflective structure 112. In someembodiments, the height H₁ is in the range of from about 1 μm to about 5μm (such as about 3 μm), and the height H₂ is in the range of from about1 μm to about 8 μm (such as about 6 μm).

In FIG. 2, contact pads 114 are formed on the second reflectivestructure 112. The contact pads 114 are physically and electricallyconnected to the second reflective structure 112, which itself isphysically and electrically connected to the emitting semiconductorregion 110. The contact pads 114 thus connect to the n-type side of thelaser diodes. The contact pads 114 may be a single layer, or may be acomposite layer that includes multiple sub-layers (shown with a dashedline) formed of different materials. In some embodiments, the contactpads 114 are formed from Ge, Au, GeAu, Ni, Ti, Ta, Pt, Cu, Al, W, In,Ag, Sn, Zn, Pd, Mn, Sb, Be, Mg, Si, the like, or combinations thereof.In embodiments where the second reflective structure 112 is formed fromn-type doped GaAs, the contact pads 114 may include at least a layer ofAu, GeAu, or Ni. For example, the contact pads 114 may be a single layerof Au, GeAu, or Ni, or a composite layer with the bottommost sub-layerbeing an Au, GeAu, or Ni sub-layer and upper layer(s) being differentconductive material(s). The contact pads 114 may be formed to any widthW₁. In some embodiments, the width W₁ is in the range of from about 8 μmto about 28 μm (such as about 12 μm).

As an example to form the contact pads 114, a photoresist is formed andpatterned over the second reflective structure 112. The photoresist maybe formed by spin coating or the like and may be exposed to light forpatterning. The pattern of the photoresist corresponds to the contactpads 114. The patterning forms openings through the photoresist toexpose regions of the second reflective structure 112. A conductivematerial is formed in the openings of the photoresist and on the exposedportions of the second reflective structure 112. The conductive materialmay be formed by a deposition process, such as physical vapor deposition(PVD), electron-beam PVD, or the like. Then, the photoresist and excessportions of the conductive material are removed. The photoresist andexcess portions of the conductive material may be removed by anacceptable lift-off process, such as ashing with an oxygen plasma or thelike.

The contact pads 114 are referred to as ohmic contacts for the laserdiodes. An ohmic contact for a semiconductive material is a contact thatshares an ohmic metal-semiconductor junction with the semiconductivematerial. An ohmic metal-semiconductor junction has a constant ratio ofcurrent to voltage during operation. The materials of the secondreflective structure 112 and contact pads 114 (in particular, their workfunctions) determine whether their metal-semiconductor junction is anohmic junction or a Schottky junction. When the work function of themetal (e.g., contact pads 114) is less than the work function of thesemiconductive material (e.g., second reflective structure 112), thejunction is an ohmic junction. When the work function of the metal(e.g., contact pads 114) is greater than the work function of thesemiconductive material (e.g., second reflective structure 112), thejunction is a Schottky junction. The work function of the material(s) ofthe contact pads 114 is less than the work function of the material(s)of the second reflective structure 112.

In FIG. 3, passivation features 116 are formed on the contact pads 114and second reflective structure 112. The passivation features 116protect the contact pads 114 and act as an etching mask duringsubsequent processing. The passivation features 116 may be formed to anywidth W₂. In some embodiments, the width W₂ is in the range of fromabout 10 μm to about 30 μm (such as about 13 μm). As an example to formthe passivation features 116, a hardmask layer is formed on the contactpads 114 and second reflective structure 112. The hardmask layer may beformed from an inorganic material, which may be a nitride (such assilicon nitride), an oxide (such as silicon oxide or aluminum oxide),the like, or combinations thereof, and may be formed by a depositionprocess such as CVD, atomic layer deposition (ALD), or the like. In someembodiments, the hardmask layer is an oxide. A photoresist is thenformed and patterned on the hardmask layer. The photoresist may beformed by spin coating or the like and may be exposed to light forpatterning. The pattern of the photoresist corresponds to thepassivation features 116. The patterning forms openings through thephotoresist. The patterned photoresist is then used in an etchingprocess, such as an anisotropic wet or dry etch, to pattern the hardmasklayer, with remaining portions of the hardmask layer forming thepassivation features 116. The photoresist may then be removed by anacceptable ashing or stripping process, such as using an oxygen plasmaor the like.

In FIG. 4, openings 118 are formed in the second reflective structure112, emitting semiconductor region 110, and first reflective structure108. The remaining mesas are referred to as laser diodes 120. The laserdiodes 120 are PIN diodes. The openings 118 may be formed by anacceptable etching process using, for example, an anisotropic dry etch.The passivation features 116 are used as a mask during the etchingprocess, and the etch stop layer(s) 106 are used to stop the etchingprocess. A cleaning process may be performed to remove excess materialafter the etching process. For example, a wet etch using dilutehydrofluoric (dHF) acid may be performed to remove excess material.

The laser diodes 120 are spaced apart from one another by a distance D₁,which is determined by the widths of the openings 118. In someembodiments, the distance D₁ is in the range of from about 4 μm to about100 μm. Further, the laser diodes 120 are formed with a tapered shape.Lower portions of the first reflective structures 108 have a lower widthW_(L), and upper portions of the second reflective structures 112 havean upper width W_(U). In some embodiments, the lower width W_(L) is inthe range of from about 10 μm to about 30 μm (such as about 14 μm), andthe upper width W_(U) is in the range of from 12 μm to about 32 μm.

In FIG. 5, protective spacers 122 are formed on sides of the laserdiodes 120. The protective spacers 122 may be formed from a dielectricmaterial such as SiN, SiO_(x), Al₂O₃, AlN, a combination thereof, or thelike. The protective spacers 122 may be formed by a conformal depositionfollowed by an anisotropic etch. For example, a deposition process suchas CVD, ALD, or the like may be used to deposit the protective spacers122.

Further, opaque portions 110B are formed in the emitting semiconductorregions 110. The opaque portions 110B are at sides of the laser diodes120, e.g., the opaque portions 110B extend around the perimeter oftransparent portions 110A of the emitting semiconductor regions 110 in atop-down view. The opaque portions 110B substantially block or absorblight from the emitting semiconductor region 110, such that the light isnot emitted from the resulting laser diodes in lateral direction (e.g.,in a direction parallel to a major surface of the carrier substrate102). The opaque portions 110B and reflective structures 108 and 112form the resonant cavity of the laser diodes 120. The opaque portions110B are oxidized material of the emitting semiconductor regions 110,and may be formed by a oxidation process such as a rapid thermaloxidation (RTO) process, a chemical oxidation process, a rapid thermalanneal (RTA) performed in an oxygen-containing environment, or the like.

In FIG. 6, the passivation features 116 are patterned with openings 124exposing the contact pads 114. The patterning may be by an acceptableprocess, such as by an etching process when the passivation features 116are an oxide material. For example, a photoresist may be formed andpatterned on the passivation features 116. The photoresist may be formedby spin coating or the like and may be exposed to light for patterning.The pattern of the photoresist corresponds to the passivation features116. The patterning forms openings through the photoresist. Thepatterned photoresist is then used in an etching process, such as ananisotropic wet or dry etch, to form the openings 124 through thepassivation features 116, exposing the contact pads 114. The openings124 may be formed to any width W₃. In some embodiments, the width W₃ isin the range of from about 6 μm to about 26 μm (such as about 11 μm).The photoresist may then be removed by an acceptable ashing or strippingprocess, such as using an oxygen plasma or the like.

In FIG. 7, UBMs 126 are formed in the openings 124 of the passivationfeatures 116. The UBMs 126 may be referred to as bonding metal layers orsimply bonding layers, and are physically and electrically coupled tothe contact pads 114. The UBMs 126 may be a single layer, or may be acomposite layer that includes multiple sub-layers (shown with a dashedline) formed of different materials. In some embodiments, the UBMs 126are formed from Ti, Ta, Ni, Cu, Sn, In, Au, Al, Pt, Pd, Ag, combinationsthereof, or the like. In embodiments where the contact pads 114 areformed from Au, GeAu, or Ni, the UBMs 126 may include at least a Tilayer. For example, the UBMs 126 may be a single layer of Ti, or acomposite layer with the bottommost sub-layer being a Ti sub-layer andupper layer(s) being different conductive material(s). The UBMs 126 maybe formed to any width W₄. In some embodiments, the width W₄ is in therange of from about 8 μm to about 28 μm (such as about 12 μm).

As an example to form the UBMs 126, a photoresist is formed andpatterned over the passivation features 116 and in the openings 118 and124. The photoresist may be formed by spin coating or the like and maybe exposed to light for patterning. The pattern of the photoresistcorresponds to the UBMs 126. The patterning forms openings through thephotoresist to expose the contact pads 114. A conductive material isformed in the openings of the photoresist and on the exposed portions ofthe contact pads 114. The conductive material may be formed by adeposition process, such as PVD, electron-beam PVD, or the like. Then,the photoresist and excess portions of the conductive material areremoved. The photoresist and excess portions of the conductive materialmay be removed by an acceptable lift-off process, such as ashing with anoxygen plasma or the like.

The UBMs 126 are formed from different material(s) than the contact pads114. In subsequent processing, conductive connectors such as solderconnectors are formed connected to the UBMs 126. The UBMs 126 act asprotective layers in the subsequent reflow processes, preventing metalinter-diffusion with the contact pads 114. The UBMs 126 are formed froma material that would form a Schottky junction if it were formeddirectly on the second reflective structure 112. In other words, thework function of the material(s) of the UBMs 126 is greater than thework function of the material(s) of the contact pads 114, and is alsogreater than the work function of the material(s) of the secondreflective structure 112. Because the contact pads 114 and UBMs 126share a metal-metal junction, no barrier is formed at the junction dueto differences in the work functions of their material(s).

FIG. 8 illustrates a cross-sectional view of a second structure 200, inaccordance with some embodiments. The second structure 200 may be adevice such as an integrated circuit, an interposer, or the like. Thesecond structure 200 includes a semiconductor substrate 202, withdevices such as transistors, diodes, capacitors, resistors, etc., formedin and/or on the semiconductor substrate 202. The devices may beinterconnected by an interconnect structure 204 formed by, for example,metallization patterns in one or more dielectric layers on thesemiconductor substrate to form an integrated circuit. The metallizationpatterns of the interconnect structure 204 include pads 204A and 204B,which may, respectively, be used for coupling to the cathodes and anodesof the laser diodes. The metallization patterns may be formed from Cu,Al, or the like. A passivation layer 206 is formed over the interconnectstructure 204 to protect the structure. The passivation layer 206 may bemade of one or more suitable dielectric materials such as silicon oxide,silicon nitride, low-k dielectrics such as carbon doped oxides,extremely low-k dielectrics such as porous carbon doped silicon dioxide,a polymer such as polyimide, solder resist, polybenzoxazole (PBO),benzocyclobutene (BCB), molding compound, the like, or a combinationthereof.

The second structure 200 further includes contact pads 208, such asaluminum or copper pads or pillars, to which external connections aremade. The contact pads 208 are on what may be referred to as respectiveactive sides of the second structure 200, and may be formed extendingthrough the passivation layer 206 by, e.g., photolithography, etching,and plating processes. The contact pads 208 may be formed from aconductive material such as Cu, Ni, Ti, or the like. In someembodiments, the contact pads 208 are multilayered, e.g., the contactpads 208 include a copper layer on a nickel layer, with the copper layerand the nickel layer each being about 1 μm thick.

Conductive connectors 210 are formed on the contact pads 208. Theconductive connectors 210 may be formed from a conductive material suchas solder, copper, aluminum, gold, nickel, silver, palladium, tin,bismuth, the like, or a combination thereof. In some embodiments, theconductive connectors 210 are solder connections, such as lead-freesolder. In some embodiments, the conductive connectors 210 are formed byinitially forming a layer of solder on the contact pads 208 throughmethods such as evaporation, electroplating, printing, solder transfer,ball placement, or the like. Once a layer of solder has been formed onthe contact pads 208, a reflow may be performed in order to shape thematerial into desired bump shapes. The conductive connectors 210 mayhave any height. In some embodiments, the conductive connectors 210 havea height of about 3 μm.

FIGS. 9 through 21 illustrate various cross-sectional view of a processfor forming a laser device package 300, in accordance with someembodiments. The laser device package 300 may be packaged with adetector in further processing to form, e.g., an image sensor, a fiberoptic networking device, or the like. The resulting device may be partof an integrated circuit device, such as a system-on-chip (SoC).

In FIG. 9, the first structure 100 is connected to the second structure200. After the laser devices 104 are attached, the laser devices 104,conductive connectors 210, and portions of the contact pads 208 abovethe passivation layer 206 have a combined height H₃. In someembodiments, the combined height H₃ is in the range of from about 3 μmto about 35 μm (such as about 14 μm).

The laser devices 104 of the first structure 100 are connected to thecontact pads 208 of the second structure 200 with the conductiveconnectors 210. The conductive connectors 210 may be contacted to theUBMs 126, and a reflow performed to physically and electrically couplethe UBMs 126 and conductive connectors 210. The UBMs 126 act asprotective layers during the reflow, preventing metal inter-diffusionbetween the conductive connectors 210 and contact pads 114. As a result,during the reflow, less metal inter-diffusion occurs at the interface104A of the UBMs 126 and contact pads 114 than at the interface 104B ofthe UBMs 126 and conductive connectors 210. In some embodiments, aninter-metallic compound (IMC) may be formed at the interface 104B, butsubstantially no IMCs may be formed at the interface 104A (e.g., theinterface of the UBMs 126 and the contact pads 114 may be substantiallyfree from IMCs). By avoiding metal inter-diffusion with the contact pads114, the junctions of the contact pads 114 and second reflectivestructures 112 retain their ohmic properties. In other words, the workfunction of the material(s) of the contact pads 114 is the same beforeand after the reflow.

When the first structure 100 is connected to the second structure 200,the second reflective structures 112 (e.g., n-type sides or cathodes) ofthe laser devices 104 face towards the second structure 200, and thefirst reflective structures 108 (e.g., p-type sides or anodes) of thelaser devices 104 face towards the carrier substrate 102. Thus, thecathodes of the laser devices 104 are connected to the pads 204A of theinterconnect structure 204. As noted above, the first reflectivestructures 108 have a lower reflectivity than the second reflectivestructures 112. As such, the produced laser beam from the emittingsemiconductor region 110 is reflected by the second reflectivestructures 112. Some of the reflected laser beam is further reflected bythe first reflective structure 108, and some is transmitted through thefirst reflective structure 108.

After the first structure 100 is connected to the second structure 200,an underfill 302 may be formed between the structures. The underfill 302may be formed from a molding compound, an epoxy, or the like. Theunderfill 302 may not be cured, and is used as a temporary support forthe second structure 200 during subsequent processing. Refraining fromcuring the underfill 302 may allow it to be more easily removed whensubsequent processing is completed.

In FIG. 10, the carrier substrate 102 is removed, leaving behind thelaser devices 104 and etch stop layer(s) 106. The carrier substrate 102may be removed by an etching process, such as a wet etch that isselective to the material of the carrier substrate 102 (e.g., GaAs). Theetch stop layer(s) 106 may stop the etching process. The underfill 302supports the etch stop layer(s) 106, preventing them from collapsingduring removal of the carrier substrate 102.

In FIG. 11, the etch stop layer(s) 106 are removed, leaving behind thelaser devices 104. The etch stop layer(s) 106 may be removed by anetching process, such as a wet etch that is selective to the material ofthe carrier substrate 102 (e.g., GaAs). The underfill 302 is alsoremoved, e.g., by an etching process such as a wet or dry etch. Afterthe removal processes, the laser devices 104 remain.

In FIG. 12, a passivation layer 304 is formed over the laser devices 104and passivation layer 206. The passivation layer 304 also extends alongsides of the contact pads 208 and conductive connectors 210. Thepassivation layer 304 may be formed from silicon oxide, silicon nitride,or the like, and may be formed by a deposition process such as CVD, ALD,or the like. In some embodiments, the passivation layer 304 is formedfrom an oxide (such as silicon oxide), and is formed by ALD. Thepassivation layer 304 is formed to a thickness T₁. In some embodiments,the thickness T₁ is in the range of from about 0.01 μm to about 0.5 μm.

Further, an isolation material 306 is formed over the passivation layer304. The isolation material 306 may be formed from an oxide (such assilicon oxide), a polymer (such as a polyimide, a low temperaturepolyimide (LTPI), PBO, or BCB), or the like. In embodiments where theisolation material 306 is an oxide, it may be formed by a depositionprocess such as CVD, ALD, or the like. In embodiments where theisolation material 306 is a polymer, it may be formed by a coatingprocess such as spin coating. The isolation material 306 is formed to athickness T₂, which is greater than the thickness T₁ of the passivationlayer 304. In some embodiments, the thickness T₂ is in the range of fromabout 3 μm to about 100 μm. The isolation material 306 surrounds andburies the laser devices 104. Portions of the isolation material 306over the laser devices 104 have a thickness T₃. In some embodiments, thethickness T₃ is less than or equal to about 65 μm.

In FIG. 13, a planarization process is performed to planarize and thinthe isolation material 306. In particular, the amount of isolationmaterial 306 over the laser devices 104 is reduced. The planarizationprocess may be, e.g., a grinding process, a chemical-mechanical polish(CMP) process, or the like. After planarization and thinning, portionsof the isolation material 306 over the laser devices 104 have a reducedthickness T₄, which is less than the thickness T₃. In some embodiments,the reduced thickness T₄ is less than or equal to about 5 μm (such asabout 1 μm).

In FIG. 14, a mask layer 308 is formed on the isolation material 306. Insome embodiments, the mask layer 308 is formed from a metal or ametal-containing material such as Ti, Cu, TiW, TaN, TiN, combinationsthereof, or multilayers thereof. In some embodiments, the mask layer 308is formed from a dielectric material such as SiC or the like. The masklayer 308 may be referred to as a hardmask layer. The mask layer 308 maybe formed by a deposition process such as PVD, CVD, or the like.

In FIG. 15, openings 310 are formed in the mask layer 308, isolationmaterial 306, passivation layer 304, and passivation layer 206. The pads204B of the interconnect structure 204 are exposed by the openings 310.The openings 310 may be formed by a two-step etching process, where themask layer 308 is patterned in a first etching process, and the patternof the mask layer 308 is transferred to underlying features in a secondetching process. As an example to the two-step etching process, aphotoresist is formed and patterned over the mask layer 308. Thephotoresist may be formed by spin coating or the like and may be exposedto light for patterning. The pattern of the photoresist corresponds tothe openings 310. The mask layer 308 is patterned by transferring thepattern of the photoresist to the mask layer 308. The mask layer 308 maybe patterned by an acceptable etching process, such as by wet etching,dry etching, or a combination thereof, using the patterned photoresistas an etching mask. The isolation material 306, passivation layer 304,and passivation layer 206 are then patterned by transferring the patternof the mask layer 308 to underlying features. The isolation material306, passivation layer 304, and passivation layer 206 may be patternedby an acceptable etching process, such as by dry etching, plasmaetching, or a combination thereof, using the patterned mask layer 308 asan etching mask. In some embodiments, the mask layer 308 may be removedbefore subsequent processing is performed. In the embodiment shown, themask layer 308 remains, and is removed after subsequent processing stepsare performed.

The openings 310 may be formed to any width W₅. The two-step etchingprocess allows the width W₅ of the openings 310 to have a small criticaldimension. In some embodiments, the width W₅ is in the range of fromabout 1 μm to about 80 μm (such as about 3 μm). Further, the openings310 may be formed to any depth D₂. In some embodiments, the depth D₂ isin the range of from about 3 μm to about 41 μm (such as about 14 μm).The two-step etching process allows the depth-to-width ratio of theopenings 310 to be large. In some embodiments, the depth-to-width ratioof the openings 310 is in the range of from about 40:1 to about 2:1.

In FIG. 16, a seed layer 312 is formed in the openings 310 and on thepads 204B of the interconnect structure 204. In embodiments where themask layer 308 remains, the seed layer 312 also extends along the masklayer 308. The seed layer 312 is a metal layer, which may be a singlelayer or a composite layer including a plurality of sub-layers formed ofdifferent materials. In some embodiments, the seed layer 312 includes atitanium layer and a copper layer over the titanium layer. The seedlayer 312 may be formed by a deposition process such as PVD or the like.A barrier layer may also be formed over the seed layer 312. The barrierlayer may be formed from TaN, TiN, or the like, and may be formed by adeposition process such as PVD or the like.

In FIG. 17, a conductive material 314 is formed on the seed layer 312and in the openings 310. The conductive material 314 may be a metal suchas copper, tungsten, aluminum, titanium, or the like. The conductivematerial 314 may be formed by plating, such as electroplating orelectroless plating, or the like.

In FIG. 18, a planarization process is performed to planarize theconductive material 314 and isolation material 306. The planarizationprocess may be, e.g., a grinding process, a CMP process, or the like.Remaining portions of the conductive material 314 and seed layer 312form conductive vias 316 in the openings 310. The conductive vias 316are physically and electrically connected to the pads 204B of theinterconnect structure 204.

In FIG. 19, openings 318 are formed in the isolation material 306 andpassivation layer 304, exposing the laser devices 104. The openings 318may be formed by acceptable photolithography and etching techniques. Forexample, a photoresist may be formed and patterned over the isolationmaterial 306. The photoresist may be formed by spin coating or the likeand may be exposed to light for patterning. The pattern of thephotoresist corresponds to the openings 318. The isolation material 306and passivation layer 304 are patterned by transferring the pattern ofthe photoresist to the isolation material 306 and passivation layer 304.The openings 318 are shallower than the openings 310, and so use of anadditional hardmask during the etching may be avoided. The isolationmaterial 306 and passivation layer 304 may be patterned by an acceptableetching process, such as by dry etching, using the patterned photoresistas an etching mask. The openings 318 may be formed to any width W₆. Insome embodiments, the width W₆ is in the range of from about 10 μm toabout 30 μm (such as about 13 μm).

In FIG. 20, electrodes 320 are formed in the openings 318 and along thetop surface of the isolation material 306, thereby forming contacts forthe first reflective structures 108 of the laser devices 104. Inaddition to being contacts for the first reflective structures 108 ofthe laser devices 104, the electrodes 320 connect the laser devices 104to the conductive vias 316. Thus, the pads 204A of the interconnectstructure 204 are electrically connected to the second reflectivestructures 112 (e.g., cathodes) through the conductive connectors 210,and the pads 204B of the interconnect structure 204 are electricallyconnected to the first reflective structures 108 (e.g., anodes) throughthe electrodes 320 and conductive vias 316.

Like the contact pads 114, the electrodes 320 are formed of a materialthat allows the metal-semiconductor junction of the electrodes 320 andfirst reflective structures 108 to be ohmic. The electrodes 320 may be asingle layer, or may be a composite layer that includes multiplesub-layers (shown with a dashed line) formed of different materials. Insome embodiments, the electrodes 320 are formed from Ti, Pt, Au, Cu, Al,Ni, combinations thereof, or the like. In embodiments where the firstreflective structures 108 are formed from p-type doped GaAs, theelectrodes 320 may include at least a Ti or Pt layer. For example, theelectrodes 320 may be a single layer of Ti or Pt, or a composite layerwith the bottommost sub-layer being a Ti or Pt sub-layer and upperlayer(s) being different conductive material(s).

As an example to form the electrodes 320, a photoresist is formed andpatterned over the isolation material 306 and laser devices 104. Thephotoresist may be formed by spin coating or the like and may be exposedto light for patterning. The pattern of the photoresist corresponds tothe electrodes 320. The patterning forms openings through thephotoresist to expose the first reflective structures 108. A conductivematerial is formed in the openings of the photoresist and on the exposedportions of the first reflective structures 108. The conductive materialmay be formed by a deposition process, such as PVD, electron-beam PVD,or the like. Then, the photoresist and excess portions of the conductivematerial are removed. The photoresist and excess portions of theconductive material may be removed by an acceptable lift-off process,such as ashing with an oxygen plasma or the like.

In FIG. 21, a passivation layer 322 is formed over the electrodes 320and isolation material 306. The passivation layer 322 may be formed fromsilicon oxide, silicon nitride, or the like, and may be formed by adeposition process such as CVD. In some embodiments, the passivationlayer 322 is formed from a nitride (such as silicon oxide).

FIG. 22 illustrates operation of the laser device package 300, inaccordance with some embodiments. The laser device package 300 may beused as a laser beam source for a depth sensor 400. Laser beam(s) may begenerated by the laser devices 104 of the laser device package 300 inpulses, and may be received by a detector 402 after being reflected by atarget 404. A round trip time for the laser beam(s) may be measured andused to calculate the distance between the depth sensor 400 and thetarget 404. The detector 402 may be, e.g., a CMOS image sensor such as aphotodiode. In some embodiments, the detector 402 is formed on a samesubstrate as the laser device package 300. For example, the detector 402may be formed in the semiconductor substrate 202 of the second structure200 (see FIG. 8).

Embodiments may achieve advantages. By selecting a desirable materialfor the contact pads 114, the metal-semiconductor junction of the secondreflective structure 112 and contact pads 114 may be ohmic (or at leastmay have a lower Schottky barrier). By forming the UBMs 126 between thecontact pads 114 and conductive connectors 210, metal inter-diffusionbetween the contact pads 114 and conductive connectors 210 may beavoided. The junctions of the contact pads 114 and second reflectivestructures 112 may thus retain their ohmic properties when reflowing theconductive connectors 210. The contact resistance of the contact pads114 may thus be reduced, and the quality and/or reliability of theresulting joint may be increased.

In an embodiment, a device includes: a first reflective structureincluding first doped layers of a semiconductive material, alternatingones of the first doped layers being doped with a p-type dopant; asecond reflective structure including second doped layers of thesemiconductive material, alternating ones of the second doped layersbeing doped with a n-type dopant; an emitting semiconductor regiondisposed between the first reflective structure and the secondreflective structure; a contact pad on the second reflective structure,a work function of the contact pad being less than a work function ofthe second reflective structure; a bonding layer on the contact pad, awork function of the bonding layer being greater than the work functionof the second reflective structure; and a conductive connector on thebonding layer.

In some embodiments, the device further includes: a passivation featureon the second reflective structure and the contact pad, the bondinglayer extending through the passivation feature. In some embodiments ofthe device, the semiconductive material is GaAs. In some embodiments ofthe device, the contact pad is a single layer of Au, GeAu, or Ni. Insome embodiments of the device, the contact pad includes: a firstsub-layer on the second reflective structure, the first sub-layer beingAu, GeAu, or Ni; and a second sub-layer on the first sub-layer, thesecond sub-layer being a different conductive material than the firstsub-layer. In some embodiments of the device, the bonding layer is asingle layer of Ti. In some embodiments of the device, the bonding layerincludes: a first sub-layer on the contact pad, the first sub-layerbeing Ti; and a second sub-layer on the first sub-layer, the secondsub-layer being a different conductive material than the firstsub-layer. In some embodiments, the device further includes: aninterconnect structure including a first pad and a second pad, the firstpad being connected to the conductive connector; a conductive viaconnected to the second pad; an electrode connecting the conductive viato the first reflective structure; and a passivation layer on theelectrode. In some embodiments, the device further includes: anisolation material surrounding the conductive via, the first reflectivestructure, and the second reflective structure, the electrode beingdisposed on the isolation material.

In an embodiment, a method includes: forming a first reflectivestructure on a substrate, the first reflective structure including firstdoped layers of a semiconductive material, alternating ones of the firstdoped layers being doped with a p-type dopant; forming an emittingsemiconductor region on the first reflective structure; forming a secondreflective structure on the emitting semiconductor region, the secondreflective structure including second doped layers of the semiconductivematerial, alternating ones of the second doped layers being doped with an-type dopant; depositing a contact pad on the second reflectivestructure, a work function of the contact pad being less than a workfunction of the second reflective structure; depositing a bonding layeron the contact pad, a work function of the bonding layer being greaterthan the work function of the second reflective structure; forming aconductive connector on the bonding layer; and reflowing the conductiveconnector.

In some embodiments, the method further includes: forming a passivationfeature on the second reflective structure and the contact pad; andpatterning an opening in the passivation feature, the bonding layerbeing deposited in the opening. In some embodiments, the method furtherincludes: etching the second reflective structure, the emittingsemiconductor region, and the first reflective structure using thepassivation feature as an etching mask, where after the etching,remaining portions of the second reflective structure, the emittingsemiconductor region, and the first reflective structure form a laserdiode, the laser diode having an upper width and a lower width, theupper width being less than the lower width. In some embodiments, themethod further includes: oxidizing the laser diode, the oxidizingforming an opaque portion of the emitting semiconductor region at sidesof the laser diode.

In an embodiment, a method includes: contacting a laser device to aconductive connector, the laser device including: a laser diodeincluding a doped semiconductive material, the laser diode having ananode and a cathode; a contact pad on the cathode of the laser diode,the contact pad and the laser diode having an ohmic junction; and abonding layer on the contact pad, the conductive connector beingcontacted to the bonding layer; reflowing the conductive connector,where during the reflowing, an inter-metallic compound is formed at aninterface of the bonding layer and the conductive connector, and nointer-metallic compounds are formed at an interface of the bonding layerand the contact pad; forming an isolation material around the laserdevice and the conductive connector; forming a conductive via throughthe isolation material; and forming an electrode connecting theconductive via to the anode of the laser diode.

In some embodiments, the method further includes: after contacting thelaser device to the conductive connector, forming an underfill aroundthe laser device; and before forming the isolation material, removingthe underfill. In some embodiments of the method, forming the conductivevia includes: forming a mask layer on the isolation material; patterningthe mask layer with a first opening; transferring the first opening ofthe mask layer to the isolation material; forming a conductive materialin the first opening; and planarizing the conductive material and theisolation material, remaining portions of the conductive materialforming the conductive via. In some embodiments of the method, formingthe electrode includes: forming an opening in the isolation material,the opening exposing the anode of the laser diode; and depositing theelectrode in the opening, along a top surface of the isolation material,and along the conductive via. In some embodiments of the method,depositing the electrode includes: depositing a single layer of Ti orPt. In some embodiments of the method, depositing the electrodeincludes: forming a first sub-layer, the first sub-layer being Ti or Pt;and forming a second sub-layer on the first sub-layer, the secondsub-layer being a different conductive material than the firstsub-layer. In some embodiments, the method further includes: depositinga passivation layer on the electrode and the isolation material.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a first reflective structurecomprising first doped layers of a semiconductive material, alternatingones of the first doped layers being doped with a p-type dopant; asecond reflective structure comprising second doped layers of thesemiconductive material, alternating ones of the second doped layersbeing doped with a n-type dopant; an emitting semiconductor regiondisposed between the first reflective structure and the secondreflective structure; a contact pad on the second reflective structure,a work function of the contact pad being less than a work function ofthe second reflective structure; a bonding layer on the contact pad, awork function of the bonding layer being greater than the work functionof the second reflective structure; and a conductive connector on thebonding layer.
 2. The device of claim 1 further comprising: apassivation feature on the second reflective structure and the contactpad, the bonding layer extending through the passivation feature.
 3. Thedevice of claim 1, wherein the semiconductive material is GaAs.
 4. Thedevice of claim 3, wherein the contact pad is a single layer of Au,GeAu, or Ni.
 5. The device of claim 3, wherein the contact padcomprises: a first sub-layer on the second reflective structure, thefirst sub-layer being Au, GeAu, or Ni; and a second sub-layer on thefirst sub-layer, the second sub-layer being a different conductivematerial than the first sub-layer.
 6. The device of claim 3, wherein thebonding layer is a single layer of Ti.
 7. The device of claim 3, whereinthe bonding layer comprises: a first sub-layer on the contact pad, thefirst sub-layer being Ti; and a second sub-layer on the first sub-layer,the second sub-layer being a different conductive material than thefirst sub-layer.
 8. The device of claim 1 further comprising: aninterconnect structure comprising a first pad and a second pad, thefirst pad being connected to the conductive connector; a conductive viaconnected to the second pad; an electrode connecting the conductive viato the first reflective structure; and a passivation layer on theelectrode.
 9. The device of claim 8 further comprising: an isolationmaterial surrounding the conductive via, the first reflective structure,and the second reflective structure, the electrode being disposed on theisolation material.
 10. A method comprising: forming a first reflectivestructure on a substrate, the first reflective structure comprisingfirst doped layers of a semiconductive material, alternating ones of thefirst doped layers being doped with a p-type dopant; forming an emittingsemiconductor region on the first reflective structure; forming a secondreflective structure on the emitting semiconductor region, the secondreflective structure comprising second doped layers of thesemiconductive material, alternating ones of the second doped layersbeing doped with a n-type dopant; depositing a contact pad on the secondreflective structure, a work function of the contact pad being less thana work function of the second reflective structure; depositing a bondinglayer on the contact pad, a work function of the bonding layer beinggreater than the work function of the second reflective structure;forming a conductive connector on the bonding layer; and reflowing theconductive connector.
 11. The method of claim 10 further comprising:forming a passivation feature on the second reflective structure and thecontact pad; and patterning an opening in the passivation feature, thebonding layer being deposited in the opening.
 12. The method of claim 11further comprising: etching the second reflective structure, theemitting semiconductor region, and the first reflective structure usingthe passivation feature as an etching mask, wherein after the etching,remaining portions of the second reflective structure, the emittingsemiconductor region, and the first reflective structure form a laserdiode, the laser diode having an upper width and a lower width, theupper width being less than the lower width.
 13. The method of claim 12further comprising: oxidizing the laser diode, the oxidizing forming anopaque portion of the emitting semiconductor region at sides of thelaser diode.
 14. A method comprising: contacting a laser device to aconductive connector, the laser device comprising: a laser diodecomprising a doped semiconductive material, the laser diode having ananode and a cathode; a contact pad on the cathode of the laser diode,the contact pad and the laser diode having an ohmic junction; and abonding layer on the contact pad, the conductive connector beingcontacted to the bonding layer; reflowing the conductive connector,wherein during the reflowing, an inter-metallic compound is formed at aninterface of the bonding layer and the conductive connector, and nointer-metallic compounds are formed at an interface of the bonding layerand the contact pad; forming an isolation material around the laserdevice and the conductive connector; forming a conductive via throughthe isolation material; and forming an electrode connecting theconductive via to the anode of the laser diode.
 15. The method of claim14 further comprising: after contacting the laser device to theconductive connector, forming an underfill around the laser device; andbefore forming the isolation material, removing the underfill.
 16. Themethod of claim 14, wherein forming the conductive via comprises:forming a mask layer on the isolation material; patterning the masklayer with a first opening; transferring the first opening of the masklayer to the isolation material; forming a conductive material in thefirst opening; and planarizing the conductive material and the isolationmaterial, remaining portions of the conductive material forming theconductive via.
 17. The method of claim 14, wherein forming theelectrode comprises: forming an opening in the isolation material, theopening exposing the anode of the laser diode; and depositing theelectrode in the opening, along a top surface of the isolation material,and along the conductive via.
 18. The method of claim 17, whereindepositing the electrode comprises: depositing a single layer of Ti orPt.
 19. The method of claim 17, wherein depositing the electrodecomprises: forming a first sub-layer, the first sub-layer being Ti orPt; and forming a second sub-layer on the first sub-layer, the secondsub-layer being a different conductive material than the firstsub-layer.
 20. The method of claim 14 further comprising: depositing apassivation layer on the electrode and the isolation material.